The long-term objective is to understand patterns of gene organization and expression in the neuroendocrine system, particularly in the hypothalamic-pituitary axis. Our present concepts of neural regulation of the anterior pitutary center on a diverse set of small neuropeptides, the hypothalamic hypophysiotropic peptides, which subserve an important role in intercellular communication by mediating endocrine responses to neural stimuli. Molecular cloning has been used to isolate and characterize cDNAs and genes encoding the precursors to two of these peptides, growth hormone-releasing factor (GRF) and corticotropin-releasing factor (CRF), which regulate the synthesis and secretion of pituitary growth hormone and corticotropin, respectively. These cloned probes will now be used to examine in a sophisticated fashion the mechanisms by which the biosynthesis of these neuropeptides is regulated during normal growth, in response to stress, and in various pathophysiological processes. Specifically, in situ hybridization will be used to detect GRF and CRF mRNAs in individual neuronal pathways in the rat hypothalamus, and changes in the abundance of these mRNAs following treatment with potential regulatory hormones or neurotransmitters determined. Changes in the expression of these genes will also be measured in response to various physiological perturbations and as a function of development. To begin to decipher mechanisms by which these genes are regulated, GRF and CRF genes and gene-fusions will be transfected into mammalian cells of both neuronal and non-neuronal origin, where their transcriptional activity and tissue-specificity can be assessed. To gain insights into the physiological function of GRF in growth control, an established strain of transgenic mice that express a GRF fusion gene and grow to be abnormally large will be further characterized to analyze tissue-specificity of transgene expression and to elucidate the role of GRF as a somatotrope growth factor. The use of GRF and CRF gene promoters for targeting hypothalamic-specific expression of genes in transgenic animals will be investigated.